Understanding - Advanced, exercise 5

Text

The variable my_string_id contains a string of ten 0-9 digits (e.g. "0000123456"). Study the execution of the following functions when they are called as follows: s(prepare(my_string_id)).

def prepare(s):
    n_list = list()

    support = ["9", "8", "7", "6", "5", "4", "3", "2", "1", "0"]

    for idx, c in enumerate(s):
        if c == "0" or c == "9":
            n_list.append(support[idx])
        else:
            n_list.append(c)

    return n_list


def s(n_list):
    list_r = list(range(len(n_list)))
    iters = list_r[1:]

    for iter in reversed(iters):
        for idx in range(iter):
            if n_list[idx] > n_list[idx + 1]:
                tmp = n_list[idx]
                n_list[idx] = n_list[idx + 1]
                n_list[idx + 1] = tmp

    return n_list

Hints

The function prepare takes the 0-9 digit string in input and returns a list prepared appropriately by consider the input digits. Instead, the function s acts upon the list returned by the previous function and modifies the order of its elements.

Additional material

The runnable Python file is available online. You can run it executing the command python exercise_5.py in a shell, and then following the instructions on screen to specify the intended input.